Well cementing compositions



ments, to Halliburton Company, a corporation of Delaware No Drawing.Original application July 7, 1958, Ser. No. 746,585, now Patent No.3,036,633, dated May 29,

1962. Divided and this application Nov. 15, 1961, Ser. No. 154,098

5 Claims. (Cl. 106-96) This application is a division of my copendingapplication Serial No. 746,585, filed July 7, 1958, now US. Patent3,036,633.

This invention relates to cement compositions and is concerned withproviding such a composition useful for various cementing purposesduring and following the drilling of oil and gas wells.

The art of oil and gas well cementing is a highly developed one.Cement-water slurries, with or without various additives, have been usedfor many years in cementing procedures carried out from time to timeduring the drilling of and the productive life of a well. Cementing isoften applied during drilling and completion procedures in connectionwith protection of production zones, isolation and confinement of waterzones, support of bore hole wall, anchorage of casing, and control oflost circulation not overcome by methods associated with the circulationof drilling mud. Such cementing procedures are ordinarily regarded asbeing of primary character. Other cementing procedures are of asecondary nature, in that they involve additions to or repairs of theprimary cementing.

These general purposes of cementing in oil and gas well practice andvarious methods for inserting and applying the cement in slurry form arewell known to those skilled in the art.

The cement employed in a cement-water slurry is of inorganic type, suchas ordinary Portland cement and variations thereof. The additives thatare often included in the slurry to obtain results not possible with thecementwater mix alone, may take the form of extenders, accelerators,retarders, reinforcing agents, and materials which increase or decreasethe weight of the slurry.

This invention is concerned with such a cement-water slurry whosecharacteristics are altered beneficially by the addition of an agent notheretofore employed as an additive, even though used extensively as alost circulation material with both oil base (Larsen Patent No.2,597,085 and Miller No. 2,773,670) and aqueous (Mayhew Patent No.2,812,161) drilling fluids and suggested as an ingredient of anearth-consolidating, thermosetting, resinforming, liquid mixture whichcements fluid-permeable, loose earth particles together at thetemperatures encountered in deep well formations, without blocking theinterstices to fluid flow (Cardwell et al. Patent No. 2,573,690).

A principal objective of the present invention is to provide an oil andgas well cementing composition of exceptionally light weight, butwithout increase in abrasiveness, such as occurs when perlite or pumiceis employed as an additive. In this connection, it should be noted thata lightweight cement-water slurry is easier to place and to hold inplace until set.

Other objectives are to provide such an oil and gas well cementing cornosition having little decrease MW over a'wm'ent-water slurry alone, buthaying a degegse in permeability porosity, density, and shgmkage p pg wose cost will not be excessive, which can be compounded from readilyaccessible materials, and which will be durable in fulfilling thevarious purposes for which such a composition is applied in practice.

CROSS REFEEERCE EXAMINER/,0

3,220,863 Patented Nov. 30, 1965 An outstanding feature of the inventionis the incorporation 0%; in discrete particle form in a cementwater srdinarily in at least equal proportion by volume with the cement.

Gilsonite is a naturally occurring asphaltite, having a specific gravitysubstantially equivalent to that of water. While it is of very lightweight in comparison to most solids, it is not porous. Unlike perlite,which is presently employed as an addition agent for the lightening ofoil and gas well cement, it does not absorb water, nor is it even wet bywater. Thus, I have found that water requirements for making anacceptable cement slurry, which may be easily placed as required andwhich will set firmly and permanently, are considerably less than thoseof perlite as an addition agent. I have found, moreover, that thestrength of the set cement is greater than with perlite.

In the present composition, the gilsonite serves as an aggregate whichlightens the cement-water slurry, imparts valuable lubricatingproperties that reduce abrasiveness of the slurry, replaces a largeportion of the cement ingredient and reduces shrinkage of the settingcement composition to an unusual extent, reduces compressibility of theset cement composition when in place, and insulates against undesirableloss or gain of heat by the well.

Additional objects and features of the invention will become apparentfrom the following detailed description of preferred formulationsthereof.

In the formulation of the cementing composition of the invention, it ispreferable to employ gilsonite in an amount ranging from approximatelyone-half to approximately ten times by volume the amount of the cementutilized, depending upon the particular result desired.

The lower range is employed where maximum strength is important; thehigher range where the various qualities imparted by the gilsonite aremost important.

Particle size and particle size distribution of the gilsonite determinethe strength and porosity-permeability characteristics of the set cementfor any given mix ratio. Where maximum strength is desirable, a coarsegilsonite aggregate should be used, for example, the following:

Percent. retained by Screen No., weight inches Min. Max.

M 0 o 4 0 5 16 2O 55 50 70 98 100 Where lightest weight and lowestporosity-permeability are important and strength is to be sacrificed oris of little importance, an aggregate of minus 50 mesh or finer may beused.

Conditions are often encountered in the field requiring variouscombinations of particle size and particle size distribution. The aboveexamples represent extremes. The mix must, however, always be pumpablethrough the system from the mixing point to the final point of placementof the cement slurry. The coarser the aggregate, the less that may bepresent in any given slurry without impeding pumpability. For example, acement-gilsonite ratio of 1:4, using the coarse aggregate specifiedabove, is difficult to pump and is likely to plug restricted passages inthe system, whereas the same mix, using the fine aggregate specifiedabove, will never plug if the water-cement ratio is high enough. Thefiner aggregate also forms, with the cement particles and with bentoniteparticles if present as an additive, a thin filter cake having a lowwater loss.

Slurry having weight as low as 8.5 pounds per gallon is obtainable usingthe higher amounts of gilsonite indicated by the aforesaid range. Itwill be realized, of course, that slurry weight will vary in accordancewith the amount of water and additives used.

As mentioned hereinbefore, slurry weight is of extreme importance formany well cementing problems. When a water zone is encountered and it isdesirable to prevent entry of water into the bore hole, an exceptionallylightweight slurry conforming to the invention will remain in placeuntil set, because its density is more nearly that of water.

Ordinary cement-water slurry has very low viscosity and is very heavy,usually weighing from 15 to 17 pounds per gallon. Drilling mud normallyweighs from 9 to 11 pounds per gallon. The closer the weight of thecement slurry is to that of the drilling mud, the less difiiculty inplacing the cement.

A bentonite-cement slurry can be made as low as 13 pounds per gallon. Byadding perlite, the weight can be brought down to somewhat under 12pounds per gallon. However, when perlite is used, disadvantages such asabrasiveness, porosity-permeability, and compressibility are introduced.

The addition of the mix of bentonite to the extent of from 1% to 8% ofthe cement present increases water requirements for the mix in making aslurry and reduces strength, but it also prevents segregation of themixed cement and gilsonite particles and helps to maintain a homogeneousmix.

Calcium chloride may be used as an additive to speed the setting, whereother additives or low temperature conditions unduly retard the set orin instances where it is desirable to prevent cement movement as earlyas possible after placement and prevent loss into thief zones.

Puzzolanes may be added to increase strength or as extenders. Otherordinarily used additives may be employed as ingredients for specificpurposes, for example, as retarders to extend the setting time of theslurry and allow additional time for mixing and pumping on lengthy jobs,or where extremely high pressures and/or temperatures are encountered,or where contaminants or additives that may unduly accelerate the setare present.

An amount of a petroleum solvent which depends upon the amount ofgilsonite present, may be added to the wet or dry mix for wetting thesurface of the gilsonite particles and causing them to form an intimatebond with casing and earth formations of the bore hole, th ventingcorrosion and minimizing pulli ng waym from the casrn ore hole wall byre ent-me shiifikagenermahmninguflhe cement "Instead of adding thesolventdirectly to the mix, it may be pumped through the casing and intothe cementing zone in advance of the gilsonite-cement slurry.

The addition of substantial quantities of gilsonite to a cement-waterslurry greatly reduces the thermal conductivity of the cement, therebyaccelerating the setting thereof and insulating the pipe from the borehole wall and from the producing zone. Such insulation of the pipe isparticularly advantageous where low pour point oils are being produced,in which instances, it is desirable to keep the temperature of the oilnear that temperature at which it issues from the producing zone.

The K factor (B.t.u.s transmitted/hr./sq. ft./inch thickness F.temperature difference) of a normal neat cement is approximately 8,while that of an 8:1 gilsonite cement is approximately 2.

It is common practice in the art to utilize a petroleum distillate asthe slurry-forming liquid instead of water. Upon placement of such aslurry in a water-bearing zone, the water displaces the distillate andeffects setting of the cement in normal manner. This practice may alsobe employed with a gilsonite cement mix conforming to the invention,provided that the time prior to displacement of the distillate by thewater is not so long as to seriously affect the gilsonite by thedissolving action of the distillate.

In this connection, it should be realized that there are gilsonites ofvarious classes with respect to melting points and solubilities. Thelower the melt point, the faster the gilsonite will dissolve in asolvent therefor or soften under conditions of heat. Therefore, the useof gilsonite in an oil and gas well cementing composition affords anopportunity to select a class of that material which best serves theparticular purpose.

The heat softening characteristic of gilsonite becomes of particularimportance in instances of relatively high bottom hole temperatures,where there is a tendency for the gilsonite to soften and diffuse intothe surrounding cement, thereby rendering it waterproof.

Whereas this invention is here described with respect to preferredspecific forms thereof, it should be understood that variousmodifications may be made without departing from the essential inventiveconcepts as defined by the claims which here follow.

I claim:

1. A composition for use in cementing a casing in a drilled well,consisting essentially of hydraulic calcareous cement; water andgilsonite as aggregate in discrete particle form, the gilsonite beingpresent in amount between about 0.5 to 10 times by volume the amount ofcement, and the proportion of water to cement and gilsonite being suchthat the mixture is a pumpable slurry capable of setting up into a solidmass.

2. A composition as claimed in claim 1, including, as an additionalingredient, a small amount of petroleum distillate.

3. A composition for use in cementing a casing in a drilled well,consisting essentially of Portland cement; water and gilsonite asaggregate, the gilsonite being in the form of discrete particles, ofwhich will pass a standard A. inch sieve and at least about 98% of whichwill be retained on a standard 100 mesh sieve, the gilsonite beingpresent in amount between about 0.5 to 10 times by volume the amount ofcement, and the proportion of water to cement and gilsonite being suchthat the mixture is a pumpable slurry capable of setting up into a solidmass.

4. A composition as claimed in claim 3, which contains about 1 to 8percent by volume of bentonite.

5. A composition as claimed in claim 3, which contains calcium chlorideto speed the setting-up of the slurry.

References Cited by the Examiner UNITED STATES PATENTS 1,744,869 1/1930Cross 106-96 2,285,302 6/1942 Patterson 166-2l 2,798,003 7/1957 Morganet al. 166-31 2,812,161 11/1957 Mayhew 106-96 2,823,753 2/1958 Hendersonet al l6629 2,880,096 3/ 1959 Hurley 16631 TOBIAS E. LEVOW, PrimaryExaminer. JOHN R. SPECK, Examiner.

1. A COMPOSITION FOR USE IN CEMENTING A CASING IN A DRILLED WELL,CONSISTING ESSENTIALLY OF HYDRAULIC CALCAREOUS CEMENT; WATER ANDGILSONITE AS AGGREGATE IN DISCRETE PARTICLE FORM, THE GILSONITE BEINGPRESENT IN AMOUNT BETWEEN ABOUT 0.5 TO 10 TIMES BY VOLUME THE AMOUNT OFCEMENT, AND THE PROPORTION OF WATER TO CEMENT AND GILSONITE BEING SUCHTHAT THE MIXTURE IS A PUMPABLE SLURRY CAPABLE OF SETTING UP INTO A SOLIDMASS.